The disclosed subject matter relates to methods, kits, and devices for detecting swelling of the brain in a patient. More particularly, the disclosed subject matter relates to methods, kits and devices configured for ensuring easy and repeatable procedures for identifying intracranial tissue swelling in order to predict when an increase in intracranial pressure (ICP) will occur. Increased ICP can arise as a consequence of various traumas, diseases or congenital defects, and can be a result of intracranial mass lesions, disorders of cerebrospinal fluid (CSF) circulation, as well as more diffuse intracranial pathological processes. For example, in some cases, increased ICP is caused by obstruction of the outflow of Cerebral Spinal Fluid (CSF). This obstruction causes the ventricles to expand resulting in hydrocephalus.
The brain typically includes four fluid-filled ventricles which are connected. These cavities, known collectively as the ventricular system, include or consist of the left and right lateral ventricles, the third ventricle, and the fourth ventricle. The fourth ventricle extends from the cerebral aqueduct (aqueduct of Sylvius) to the obex, and is filled with CSF. The fourth ventricle has a characteristic diamond shape in cross-sections of the human brain. The fourth ventricle is located within the pons or in the upper part of the medulla. CSF entering the fourth ventricle through the cerebral aqueduct can exit to the subarachnoid space of the spinal cord through two lateral foramina of Luschka and a single, midline foramen of Magendie.
The fourth ventricle is an outpouching on the posterior part of the brainstem. The flow of CSF to the nasal submucosal lymphatic channels occurs through the cribriform. When CSF pressure is elevated, cerebral blood flow may be constricted. CSF entering the fourth ventricle through the cerebral aqueduct can exit to the roof of the fourth ventricle formed by the cerebellum (and can expand into lateral, third and fourth ventricles, connected by thinner channels). Expansion of the ventricles is called Hydrocephalus and can lead to an increase in intracranial pressure. Congenital hydrocephalus is present in about 0.1% of newborn children and is due to outflow obstruction. Acquired Normal Pressure Hydrocephalus (NPH), due to excessive production of CSF, is present in an estimated 0.5% of adults over the age of 65, is underdiagnosed, and can cause gait disturbances, urinary incontinence and dementia.
Alternatively, expansion of intracranial solid tissues including: [1] brain cell swelling (cerebral edema) from infectious, hemodynamic, pharmacologic, metabolic or traumatic causes, [2] brain tumors, and [3] subdural or epidural hematomas from minor head trauma, can cause collapse of the ventricles; continued expansion results in increased ICP.
In both hydrocephalus (ventricular inflation) and intracranial tissue expansion, the first compensation is the obliteration of the layer of CSF surrounding the brain. The obliteration of this layer typically precedes an increase in ICP.
While normal ranges for ICP vary with age, increases in ICP can be acute or chronic, and thresholds for treatment are often difficult to determine.
The relation between volume and pressure within the cranium is non-linear. The Monro-Kellie hypothesis states that the sum of the intracranial volumes of blood, brain, CSF, and other components (for example, tumor, hematoma) is constant. The skull can be considered to be an inelastic container. An increase in the volume of any one of the intracranial contents is typically offset by a decrease in one or more of the others, ultimately leading to an increase in ICP. Intracranial blood (especially in the venous/venular compartment) and CSF are two low pressure components whose volume can adapt easily to accommodate an increase in the volume of intracranial contents. Once the change in volumes of intracranial blood and CSF are exhausted, further increases in volume result in increase in ICP. Changes in both arterial and venous compartments affect pressure. Sitting up to an inclined position to raise the brain 20 cm above the heart results in ICP reduction by 8 mmHg due to deflation of the veins and venules; the expansion of intracranial arteries and arterioles by about 5 milliliters after each heart beat raises ICP by 1 mmHg. Compliance (the change in volume for a given change in pressure) provides an index of compensatory reserve, with low values suggesting a diminished reserve. Compliance is reduced when ICP is elevated, at an abnormal ICP of 25 mmHg, the arterial pressure ICP pulsation is 4 mmHg.
Conventionally, emergency room personnel and intensive care practitioners could deliver better care if ICP could be measured or monitored in a patient presenting with certain conditions such as head trauma or neurological symptoms. Unfortunately, monitoring ICP is typically accomplished through the use of a manometer that is inserted into a hole drilled into the skull of the patient. Thus, monitoring ICP requires an invasive procedure undertaken by a neurosurgeon (or at least with a neurosurgeon available in case of complications or difficulties with the surgery), because the procedure exposes the patient to infection and other inherent surgical risks. In addition to the difficulty in obtaining and monitoring ICP, there are also certain drawbacks to relying solely on ICP for diagnosis and treatment of trauma. For example, relying solely on ICP data may cause a time delay in treatment, may require complicated diagnostic and monitoring protocols, and may be subject to false readings should the instrumentation for monitoring ICP not be set up correctly or otherwise fail or be interpreted improperly.